Whistle sound during slight acceleration

[LOrnskov]

Hi,
I own a 2021 M3 LR. Recently is has started to make a whistling sound when for instance driving 50 km/h and applying a slight acceleration. The sound stops as soon as I stop the acceleration and keep a constant speed.

Any suggestions on what this issue would be about?

Kind regards from Denmark

 

[MikeyC]

The description sounds like inverter whine. I don't really hear it on mine unless I'm really getting on the throttle and the car isn't warmed up yet, but your ears may be more sensitive to it than mine. FWIW, my 2017 Volt and 2019 Bolt both did that too: inverter whine at a certain speed with very light throttle. Does it only do it (or is it worse) when the car is cold? Some say the motors are run inefficiently when cold to help heat things up (and it makes that sound) but I don't know if that's true.

Mike

 

[GtiMart]

On top of the previous comment, you'll hear the whine louder if you have a dual motor and the car is preheating the battery, for example en route to a supercharger, or when the front motor gets activated for a while after the back wheels have slipped on a slippery surface. As soon as the front motor is "on", the whine is louder.

 

[LOrnskov]

Hi,
I managed to figure out the issue. After reading quite a lot, I suspected that it was coming from the rear ground strap. I tried to tighten the bolt, which made the sound level to go down by 50% or so, so that confirmed my suspicion. I then changed the setup of the screw, which was screwed into the chassis, to the actual ground strap would be 100% connected to the chassis (and not just indirectly connected via the screw into the chassis. The sound has 100% diminished.

 

[singung81]

Hi,
I managed to figure out the issue. After reading quite a lot, I suspected that it was coming from the rear ground strap. I tried to tighten the bolt, which made the sound level to go down by 50% or so, so that confirmed my suspicion. I then changed the setup of the screw, which was screwed into the chassis, to the actual ground strap would be 100% connected to the chassis (and not just indirectly connected via the screw into the chassis. The sound has 100% diminished.

Hi, I have the same issue, and tightening the ground strap made no difference. Would you please share the details of how you connect the strap directly to the chassis.

 

[LOrnskov]

Hi, I have the same issue, and tightening the ground strap made no difference. Would you please share the details of how you connect the strap directly to the chassis.

Hi,
Have you tried to uninstall the ground strap completely, and then go for a short ride to confirm that the ground strap is the issue? If you remove the ground strap from the chassis, the sound should disappear.
If the ground strap is indeed the issue, then modify the setup as enclosed picture. Grind off the bolt things so the ground strap can be connected directly to the chassis and put on a new bolt.

 

[LOrnskov]

Hi,
Have you tried to uninstall the ground strap completely, and then go for a short ride to confirm that the ground strap is the issue? If you remove the ground strap from the chassis, the sound should disappear.
If the ground strap is indeed the issue, then modify the setup as enclosed picture. Grind off the bolt things so the ground strap can be connected directly to the chassis and put on a new bolt.

 

[Gasaraki]

I wish mine sounds louder. However if you are preconditioning your battery you can hear it louder. This is normal.

 

[singung81]

Hi,
Have you tried to uninstall the ground strap completely, and then go for a short ride to confirm that the ground strap is the issue? If you remove the ground strap from the chassis, the sound should disappear.
If the ground strap is indeed the issue, then modify the setup as enclosed picture. Grind off the bolt things so the ground strap can be connected directly to the chassis and put on a new bolt.

No. I haven't done that. I'm scared to drive the car around with the ground strap off. Thank you for the picture. May I ask what tools you used to grind off that bolt thing?